Lubricating oil composition



United States Patent O 2,977,307 LUBRICATING OIL COMPOSITION Andrew D. Abbott, Ross, Calif., assignor to California Research Corporation, San Francisco, Calif., a corporation of Delaware No Drawing. Filed Mar. 31, 1958, Ser. No. 724,837 3 Claims. (Cl. 25232.7)

This invention relates to a lubricating oil having improved physical properties. More particularly, the invention is concerned with a stable viscosity mineral lubricating oil composition containing metal salt organic detergent additives in combination with polymeric thckening additives.

Polymeric additives are extensively used in mineral lubricating oil compositions to impart desirable viscositytemperature characteristics to the compositions. These additives are designed to modify lubricating oils so that changes in viscosity occurring with variations in temperature are kept as small as possible. Lubricating oils containing such polymeric additives are somewhat thickened at the higher temperatures normally encountered in engine operation while at the same time retaining desirable low viscosity fluidity at cold starting temperatures. The ability of a lubricating oil to accommodate increased temperatures with a minimum decrease in viscosity is indicated by its high viscosity index as derived from commonly accepted viscosity standards. Because of the aforementioned properties, these polymeric additives have been conveniently termed both thickeners and viscosity index improvers.

Polymers of alkyl methacrylates are particularly effective additives of the above type. Included are polyalkyl meth-acrylates in which the alkyl groups are mixtures of lower alkyl groups of 7 carbon atoms or less and higher alkyl groups of 8 carbon atoms or more. Some of the more important polymeric methacrylates also provide enhanced detergent properties to mineral lubricating oil compositions as well as desirable viscosity-temperature characteristics. Among the more important polymeric viscosity index improvers and detergents of this type are the copolymers of the aforementioned alkyl methacrylates with monomers containing polar groups such as the N,N-dialkylamino-alkylmethacrylates, the polyglycolmonomethacrylates and the vinyl nitrogen heterocycles.

Mineral lubricating oils containing polymeric additives as described above are also commonly compounded with metal salt organic detergent additives. .These metal salt additives alleviate the formation of undesirable engine deposits by giving the oil enhanced ability to maintain deposit-forming materials such as sludge and resins from oxidation in dispersion in the oil. Among the more important additives of this type are the essentially neutral alkaline earth metal petroleum sulfonates and the alkaline earth metal phenates or their 'sulfurized derivatives. Another important type of metal salt organic detergent additive, namely, the zinc dithiophosphates, imparts not only detergent characteristics but also oxidation and corrosion inhibiting properties to mineral lubricating oil compositions.

The two different classes of additives described above have been combined to give mineral lubricating oil compositions having excellent detergent properties, along with superior viscosity-temperature characteristics. Unfortunately, it happens that the addition of the important metal salt organic detergentsto. mineral lubricating oils containing the polymeric thickeners mentioned above has a decidedly'adverse effect on the viscosity-temperature characteristics of the mineral lubricating oil compositions. There is an undesirabe inc ease in the viscosity compared to the viscosity of the thickened mineral Patented Mar. 28, 1961 i V 2 v lubricating oil alone and the variations in viscosity with temperature changes of the oil are unfavorably exaggerated as indicated by the lowered viscosity index of the composition. t

The above-mentioned adverse effect on the viscositytemperature characteristics of the mineral lubricating oil compositions is of the greatest importance in the case of the so-called multigrade lubricating oils developed for more efiective lubrication over the wide temperature ranges commonly encountered in internal combustion engines. Polymeric thickeners of I the important polymethacrylate ester type are added to these oils to raise the viscosity index radically and thus enable a single oil to meet the specification viscosity ranges of two or three diiferent' SAE viscosity grades. The increase in viscosity, particularly at low temperatures where only certain viscosities can be tolerated, and the depreciation of the aforementioned critical viscosity index improvement of the thickened lubricating oil by the addition of the more important metal salt organic detergent additives referred to above may prevent an oil from qualifying as a multigrade oil.

The addition of the metal salt organic detergent additives to the thickened mineral lubricating oils has both an immediate adverse effect as described above, and also a postponed effect in that further undesirable increases in viscosity and depreciation of the viscosity index are observed over certain periods of time. This effect which has been conveniently termed viscosity drift is extremely critical since an otherwise satisfactory oil may become completely unsatisfactory during the usual storage periods for lubricating oils.

It has now been found that stable viscosity-temperature characteristics are provided in mineral lubricating oil compositions comprising a major portion of a mineral lubricating oil, a minor portion sufticient to improve the viscosity index of the mineral lubricating oil of an alkylmethacrylate polymer, a minor portion sufficient to enhance the detergent characteristics of the mineral lubricating oil of a metal salt organic detergent additive se# lected from the class consisting of neutral alkaline earth metal petroleumsulfonate, alkaline earth metal phenate,

sulfurized alkaline earth metal phenate and zinc aromatic dithiophosphate and a minor portion sufiicient to stabilize the viscosity of the mineral lubricating oil compositionof a dialkyl sulfoxide having alkyl groups of l to 3 carbon atoms each.

The mineral lubricating oil compositions of the iii-w vention possess unusually stable viscosity-temperature characteristics compared to mineral lubricating oil com- 1 positions containing polymethacrylate ester viscosity in deximprovers incombination with metal salt organic detergent additives without the dialkyl sulfoxide. "Particularly in the case of the multigrade lubricating oils where certain minimum low temperature viscosities and minimum variations in visco ity of the oil over broad temperature ranges are critical, the outstanding properties of the compositions according to the invention are most appreciated. It 'is found that the viscosity as well as the viscosity index of the present compositions remains practically unchanged, even over extended periods of time. The dialkyl sulfoxides with alkyl groups containin from 1 to 3 carbon atoms each which'are used in the to a sulfoxide group,

3 Suitable sulfoxides in this class of compounds include dimethyl sulfoxide, methyl ethyl sulfoxide, methyl propyl sulfoxide and dipropyl sulfoxide. For present purposes, the dimethyl sulfoxide is preferred since it provides the most viscosity stable compositions at lowest concentration.

The metal salt organic detergent additives of the more important types such as are employed in the mineral lubricating oil compositions according to the present invention includes the neutral alkaline earth metal petroleum sulfonates, alkaline earth metal phenates, sulfurized alkaline earth metal phenates and zinc aromatic dithiophosphates as mentioned above. These particular metallo organic additives are generally recognized as eifective lubricating oil detergents and inhibitors and should require no particular description here. Illustrative alkaline earth metal petroleum sulfonates include barium petroleum sulfonate, calcium petroleum sulfonate, magnesium petroleum sulfonate, and slightly basic calcium petroleum sulfonates having a base ratio not greater than 0.6 (base ratio being the ratio of basic calcium to total calcium). Only the substantially neutral sulfonates seem to have an adverse eifect on the thickened mineral lubricating oils. Suitable alkaline earth metal alkyl phenates and sulfurizer alkaline earth metal alkyl phenates include calcium cetylphenate, calcium tetradecylphenate, barium cetylphenate, and sulfurized calcium cetylphenate. The aforementioned phenates preferably contain from to 20 carbon atoms in the alkyl group and may be normal or basic in nature since both types alter the viscosity-temperature characteristics of the thickened oils undesirably. The zinc aromatic dithiophosphates of the compositions of the invention are characterized by the presence of at least one aryl group. Illustrative thiop-hosphates of this type include zinc dodecyl phenyl thiophosphates, zinc dihexylphenyl dithiophosphate, zinc hexyl naphthyl dithiophosphate and zinc diamylphenyl dithiophosphate. Thiophosphates without aryl groups do not appear to affect the critical viscosity properties of the thickened compositions.

The polymeric methaerylate ester lubricating oil thickeners of the compositions according to the invention are also a recognized class of efiective lubricating oil additives. In general, they are polymers of higher alkyl esters of mil-unsaturated monocarboxylic acids of from 3 to 8 carbon atoms which contain oil-solubilizing alkyl groups of at least 8 carbon atoms. Illustrative esters of these types include dodecyl methaerylate, octadecyl methaerylate, tridecylacrylate and tetradecyl crotonate. The methacrylates are presently preferred since they provide very satisfactory improvement in the viscosity indexes of lubricating oil compositions. Other, monomers, including lower alkyl methacrylates such as butyl methacrylate, may also be copolymerized with the aforementioned higher alkyl methacrylates. Polar monomers such as those characteristic of polymeric detergent additives for lubricating oils may also be included. These polymeric additives 'are also effective viscosity index improvers as well as superior detergents. The more suitable polar monomers are the N,N-dialkylaminoalkyl methacrylates such as N,N-diethylaminoethyl methaerylate, the vinyl nitrogen heterocyclic compounds such as vinyl pyridine and vinyl pyrrolidone and the polyglycol monomethacrylates such as the dodecyl ether of octadecaethyleneglycol monomethacrylate.

Polymeric methaerylate viscosity index improvers of the above-mentioned types are generally characterized by molecular weights in the range of 100,000 to 300,000 and higher. In the case of the detergent polymeric compounds, the polar monomers are ordinarily present in proportions of from about 0.1 to about 35.0% by weight of the polymer. 7

The mineral lubricating oil of the lubricant composition of the invention may be any of the usual types of base stocks are suitable. The mineral lubricating base oils may be refined by any of the conventional methods such as solvent refining or sulfuric acid refining. Solventrefined Mid-Continent paraifinic-type base stocks appear to present the greatest viscosity. stability problem and, therefore, have particular application to the compositions of the invention. 7

Further illustrations of the improved mineral lubricating oil compositions according to the present invention are provided by the following examples. Unless otherwise specified, the proportions in the examples are on a weight basis.

Several mineral lubricating oil compositions containing the typical polymethacrylate thickeners referred to above and the metal salt organic detergent additives were prepared to show the effect of the metal salt additives on the thickened mineral lubricating oil compositions. In the compositions the base oil was a Mid-Continent parafiinic 200 neutral solvent refined mineral lubricating oil having a viscosity of 200 SSU at 100 F. The oil was thickened with 6% by weight of the copolymer of a mixture of dodecyl methaerylate, octadecyl methaerylate, butylacrylate and N-vinyl-pyrrolidone in which there are approximately 65 parts by weight of the dodecyl and octadecyl methacrylates, approximately 25 parts by weight of butylacrylate and approximately 10 parts by weight of N-vinylpyrrolidone. The copolymer has an average molecular weight of approximately 150,000 to 200,000. Various metal salt detergent additives are added to the thickened mineral lubricating oil and the effect on the viscosity of the oil in Saybolt Seconds Universal (SSU) at 210 F. is observed as indicated in the following table. The proportions of the metallic salt detergent additives are given in millimoles per kilogram (rnM./kg.).

1 Tetradecyl phenate derived from a mixture of propylene tetramer and pentamer alkylated phenols having an average of approximately 14 carbon atoms in the alkyl group.

According to the above test results, it will be seen that the important metallic salt detergent additives of the alkaline earth metal petroleum sulfonate, alkaline earth metal phenate and zinc aromatic dithiophosphate types all have an adverse effect on the viscosity of the thickened mineral lubricating oil. The unusual nature of the viscosity stability problem shown by the above test data is emphasized by the fact that certain other metal salt detergent additives such as the zinc dialkyl dithiophosphates do not have any such adverse effect on the viscosity of the thickened mineral lubricating oil.

The elfect of the inclusion of dialkyl sulfoxides containing from 2 to 6 carbon atoms in the thickened mineral lubricating oil compositions containing metal salt detergent additives in accordance with this invention is shown by a number of examples. Test results illustrating the viscosity-temperature characteristics of these examples are given in the following table.

Oil A in the table is the thickened oil described above consisting of a 200 neutral solvent-refined mineral lubrieating oil containing 6% by weight of methaerylate and vinyl pyrrolidone copolymer.

. Oil B is the thickened oil plus 25 mM./kg. of calcium mineral lubricating base oils. Paraffinic or naphthenic petroleum sulfonate (base ratio 0.4) having an average from 4 to 6 carbon atoms each, (B) an ester selected from the group consisting of alkylacrylates and alkylmethacrylateshaving alkyl groups, containingfrom 12 to carbon atoms each and (C) vinyl pyrrolidone,'said copolymer having a molecular weight in the range of 100,000 to 300,000 and said vinyl pyrrolidone being from about 0.1 to about 35.0% by weight of the copolymer, from 5 to 100 millimoles per kilogram of a metal Table II Viscosity Viscosity Viscosity Viscosity Percent at 0 R, at 210 F., Increase, Correction, Improve- SSU SSU 21 210 F., ment SSU SSU A('Ihickened oil) 7, 800 63.0 B('1"nickened oil+metal salt) 33, 000 79. 5 16. 5 B('Ihickened oil+metal salt)+0.3% dimethyl sulfoxide 14, 100 69. 2 10. 3 63 C-(lhiekened oil) 2. 800 57. 2 D-(Thickened oil+rnetal salt) 8, 100 64.4 7. 2 D--(Ihickened oil+metal salt)+0.1% dimethyl sulfoxide 6, 100 61. 1 3. 3 46 In the above-described test results, addition of dialkyl sulfoxide to the lubricating oil compositions is shown to overcome substantially the adverse effect on the viscosity incurred by the addition of the metal salt to the thickened oil.

Experiments were also carried out with the mineral lubricating oil compositions of the invention to illustrate the stability of their desirable viscosity-temperature characteristics over extended periods of time, such as those encountered under normal storage conditions. A representative sample of thickened oil and metal salts, as described in connection with oil D above, was treated with dialkyl sulfoxide. The results of these tests are given in Table III as follows:

Table III Additive 0 Days 15 Days Days None 142 137 137 0.1% dimethyl sulfoxide 147 147 148 From the above test results, it is seen that the mineral lubricating oil compositions containing polymeric thickener and metal salt have unstable viscosity-temperature characteristics during storage. The viscosity indexes are;

cient to accomplish the obvious purposes of the additives as will be apparent to those skilled in the art. Expressed in numerical ranges, however, the polymeric thickening additives will be in the customary range of from 0.1 to 10.0% by weight of the composition. The metal salt will be, expressed in mM./kg., in the range of 5 to 100 mM./kg. Thealkanediol will be present in amounts in the range of from 0.05 to 1.0% by weight ofthe composition.

I claim:

1. A mineral which the aromatic groups are selected from the class lubricating oil composition comprising a consisting of alkylphenyl andalkylnaphthyl groups and from 0.05 to 1.0% by weight of dialkyl sulfoxide containing from 2 to 6 carbon atoms.

2. A lubricating oil composition comprising a major portion of a mineral lubricating oil, from 0.1 to 10.0% by weight of an oil-soluble copolymer of (A) an ester selected from group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 4 to 6 carbon atoms each, (B) an ester selected from group consisting of alkylacrylates and alkylmethacrylates having alkyl groups in the range of 12 to 20 carbon atoms each and (C) vinyl pyrrolidone, said copolymerhaving a molecular weight in the range of 100,000 to 300,000 I g and said vinyl pyrrolidone being from about 0.1 to about 3 35.0% by weight of the copolymer, from 5 to millimoles per kilogram each of neutral calcium petroleum A sulfonate, sulfurized calcium tetradecylphenate and zinc butyl hexyl dithiophosphate and from 0.05 to 1.0% by weight of dimethyl sulfoxide.

3. A lubricating oil composition comprising a major portion of a mineral lubricating oil, from 0.1 to 10.0%, by weight of an oil-soluble'copolymer of (A) an ester;

selected from the group consisting of alkylacrylates and alkylmethacrylates having alkyl groups containing from 4 to 6 carbon atoms each, (B) an ester selected from the? group consisting of alkylacrylates and alkylmethacrylates" havingalkyl groups containing from,12 to 20 carbon atoms each and (C) vinyl pyrrolidone, said copolymer" I having a molecular weightin the range'of'100,000 to 300,000 and said vinyl pyrrolidone being from about 0.1

to about 35.0% by '{weight of the'copolymer, from to 100 millimoles per kilogrameach of, neutral calciumpetroleum sulfonate and sulfurized calcium tetradecylphe-q mate and from 0.05 to 1.0 by weight of dimethyl sulfoxide.

References Cited in the file. of this patent 7 UNITED STATES PATENTS,

2,318,629 Prutton May 171,- 19 43 12,602,048' @Michaels et al J ulyf 11.1952 2,677,617 Thompson ..May4; 2,833,719"

major portion of a mineral lubricating oil, from 0.1 t i 10.0% by weight of an oil-soluble copolymer of (A) an ester selected from the group consisting of alkylacrylates. and alkylmethacrylates having alkyl groups containing 

1. A MINERAL LUBRICATING OIL COMPOSITION COMPRISING A MAJOR PORTION OF A MINERAL LUBRICATING OIL, FROM 0.1 TO 10.0% BY WEIGHT OF AN OIL-SOLUBLE COPOLYMER OF (A) AN ESTER SELECTED FROM THE GROUP CONSISTING OF ALKYLACRYLATES AND ALKYLMETHACRYLATES HAVING ALKYL GROUPS CONTAINING FROM 4 TO 6 CARBON ATOMS EACH, (B) AN ESTER SELECTED FROM THE GROUP CONSISTING OF ALKYLACRYLATES AND ALKYLMETHACRYLATES HAVING ALKYL GROUPS CONTAINING FROM 12 TO 20 CARBON ATOMS EACH AND (C) VINYL PYRROLIDONE, SAID COPOLYMER HAVING A MOLECULAR WEIGHT IN THE RANGE OF 100,000 TO 300,000 AND SAID VINYL PYRROLIDONE BEING FROM ABOUT 0.1 TO ABOUT 35.0% BY WEIGHT OF THE COPOLYMER, FROM 5 TO 100 MILLIMOLES PER KILOGRAM OF A METAL SALT ORGANIC DETERGENT ADDITIVE SELECTED FROM THE CLASS CONSISTING OF NEUTRAL ALKALINE EARTH METAL PETROLEUM SULFONATE, ALKALINE EARTH METAL PHENATE, SULFURIZED ALKALINE EARTH METAL PHENATE AND ZINC AROMATIC DITHIOPHOSPHATE IN WHICH THE AROMATIC GROUPS ARE SELECTED FROM THE CLASS CONSISTING OF ALKYLPHENYL AND ALKYLNAPHTHYL GROUPS AND FROM 0.05 TO 1.0% BY WEIGHT OF DIALKYL SULFOXIDE CONTAINING FROM 2 TO 6 CARBON ATOMS. 